1. Field of the Invention
The invention relates generally to a machine for the continuous molding of polystyrene and more particularly to improvements in such a machine wherein the apparatus for moving the polystyrene granules through the molding chamber does not define the molding chamber or limit the expansion of the polystyrene as the polystyrene granules move through the molding chamber.
2. Description of the Prior Art
Workers in the art have developed a variety of machines for the continuous molding of polystyrene granules in which granules of polystyrene containing a heat-activated expansion agent are converted into a coherent agglutinated body. In some cases, such a machine includes an open ended molding chamber. The pre-expanded polystyrene granules enter the molding chamber through the inlet end of the molding chamber and continuously move through the chamber. As the polystyrene granules move through the chamber they are subjected to heat to cause their expansion. The molding chamber operates to limit the expansion of the polystyrene and form it into a coherent agglutinated body having a generally rectangular cross section.
Norrhede et al. U.S. Pat. No. 3,383,441 and Jacob U.S. Pat. No. 3,408,690 disclose one type of continuous molding machine having a horizontal molding chamber defined by the surfaces of two opposed endless belts. A major drawback to the use of machines is that the endless belts which move the polystyrene granules through the molding chamber define the molding chamber and limit the expansion of the polystyrene granules. Thus, the endless belts must be rigid and cumbersome and require complex drive and guide mechanisms to operate properly. Generally, these belts are formed of stainless steel in either a perforated band or chain-link form. In addition, these machines are not thermally efficient because steam can leak from the molding chambers at the locations of the guides for the endless belts and at the steam chest. Because the endless belts in these machines are rigid, they cannot shape the cross section of the final product into anything other than a rectangle.
Berner U.S. Pat. No. Re. 27,964 teaches a second type of continuous molding machine wherein the molding chamber is defined by the surfaces of a rotating wheel and a stationary wall or plate. However, the polystyrene granules occasionally tend to adhere to the surface of the stationary wall or plate due to static electric charges that build up between the surfaces of the beads and the surfaces of stationary wall or plate.
Peille U.S. Pat. Nos. 3,880,559 and Re. 29,416 teach machines for the continuous molding of polyurethane. The machines include two endless belts for moving the polyurethane through the molding chamber that in part mold the polyurethane. The former machine includes rigid plates and the latter flexible mats for shaping the polyurethane. However, the machines disclosed by Peille would not satisfactorily mold polystyrene. Normally, polystyrene expansion causes pressures of between 10 and 20 psi to be exerted on the walls of the molding chamber. These pressures are much greater than those exerted by polyurethane as it expands. Thus, a molding chamber that confines polyurethane as it expands would not necessarily confine expanding polystyrene.
Accordingly, it is desirable to provide a machine for the continuous molding of polystyrene wherein the apparatus for moving the polystyrene granules through the molding chamber does not define the molding chamber or limit the expansion of the polystyrene as the polystyrene granules move through the molding chamber. Thus, the apparatus for moving the polystyrene granules through the molding chamber can be a flexible belt that would obviate the need for complex guide and drive mechanisms. Because belts are flexible, they can conform to the shape of the molding chamber and, thus, enable the final product to have a nonrectangular cross section.